The formation of production pieces out of moldable materials has historically been one of humankinds basic fabricating technologies. Traditionally, these molding techniques included shaping, casting and forging processes. In a shaping process, a moldable material is shaped or sculpted, usually by hand, into a desired configuration, and the material is then cured in some manner, such as heating or drying. In a casting process, a material to be molded is forced into a die so that it takes a selected shape, and the material is allowed to cure until the material becomes sufficiently set to retain the shape of the mold element. On the other hand, in the forging process, a malleable material is mechanically forced over the shape of a mold element so that it takes on and retains the profile thereof. It is essential in the forging process that the material be malleable or capable of being placed in a malleable or "plastic state." Certain materials used in this process are placed in a malleable or plastic state by heating so that the forging process is accomplished as a thermoforming operation. Strictly speaking, in the forging process, a material is heated and is hammered or beat into shape.
Since the advent of the "plastics age" during which various organic polymerized compounds have been utilized as a production medium, the distinctions between casting and forging have become blurred due to the versatility of the organic polymer medium. With the medium of plastic materials, three types of thermoforming processes are prevalent. One process, injection molding, may be likened to casting; injection molding is accomplished by forcing heated plastic material into a three dimensional mold element, and the production piece is released from the mold element when it has taken and can retain the shape of the mold. In another process, more akin to forging, a sheet of material that is heated to a plastic state is placed between male and female dies which close on the sheet to force a portion to take on the complementary profile of the male and female dies after which the dies open so that the formed production piece may be removed. Intermediate of these two techniques are the various pressure controlled thermoforming processes such as vacuum/pressure thermoforming and blow molding. In the vacuum/pressure process, a sheet of material to be fabricated is forced to take on the profile of either a male mold element or a female mold element by applying a vacuum (or suction) to one side of the sheet and/or pressure to the opposite side of the sheet so that the pressure differential on the plastisized sheet causes the sheet to conform to the shape of the mold element without the need for a complimentary die. In blow molding, a three dimensional object is formed or "cast" out of a three dimensional production blank in the form of a closed tube or other production piece having an interior. The production piece is heated to a plastic state, inserted into a mold and pressure is applied to the interior of the piece thereby causing it to expand against the sides of a mold. Vacuum or suction may also be applied exteriorily of the production piece to enhance the molding operation.
The present invention has applications generally to the thermoforming technology. In its most general form, the present invention may be employed to form a partible port section in a production piece that has a suitable panel portion available to receive a partible port. Most dominantly, the present invention is utilized concurrently during the initial fabrication of the production piece rather than subsequently. The present invention has special application in the plastic lid industry wherein a container lid is fabricated out of a plastic material. These lids are adapted to snap-fit onto the rim of a container, such as a paper or plastic cup or glass, in order to help prevent spillage of fluids placed in the container. To this end, the lid has a perimeter having a lip structure configured to engage the rim of the container.
Often, when lids are provided for a beverage container, it is desirable to provide a port section so that a drinking straw may be inserted through the port section thus allowing access to the liquid contents therein. In some instances, a tear-away port structure is provided on the lid adjacent the perimeter thereof to provide a drink access opening for the mouth of the user. Where straw ports are provided, and as discussed more thoroughly in the detailed description of the present disclosure, a port is provided by transverse cuts which extend completely through the lid panel so that a plurality of triangular shaped flaps are cut with these flaps having a common vertex location. When a straw is inserted through the port, then, the flaps bend interiorily of the container so that the effective port size increases. A disadvantage of this structure is present, however, since the cuts are made completely through the lid; this severing of the lid violates the integrity of the lid in its ability to prohibit passage of fluid. Therefore, even before a straw is inserted through the port, liquid may be spilled out of the port section. Likewise, once the straw is inserted through the port, liquid may escape out of the parted section around the straw's outer perimeter. Where tear-away port sections are provided, it has been found difficult to use these tear-away ports because, as a result of the fabrication techniques, it is difficult to control the thickness of the lid thereby resulting in inefficient tear-away lines. Furthermore, tear-away sections once torn, permit liquid in the cup to spill if the cup is tipped.
Due to the disadvantages of the prior art techniques, a significant need has existed for a substantial period of time to develop a methodology for creating a partible port section that remains completely sealed until mechanical force is applied to part the port section from the container lid. There has also been a need for such a process to have a high degree of control so that such port sections may be formed in high speed production operations with reliability. These needs were addressed in my U.S. Pat. No. 5,151,233. The present thermoform vacuum/pressure process is also directed meeting these needs as well as to the need for creating a better relative seal between the lid and straw after insertion of the straw through the partible port section.